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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a silver halide photographic material and
a method of processing it. The present invention is applicable to the
production of rapidly processable light-sensitive materials and to their
rapid processing. Therefore, the present invention finds utility in X-ray
film applications.
2. Description of the Prior Art
The consumption of silver halide photographic materials has been increasing
in the past decade and, in order to meet the increased demand of consumers
for developing and processing photographic films, more rapid development
and processing, or an increased capability of process film within a given
period of time, is greatly needed. This tendency is also found in areas
where X-ray light-sensitive materials such as medical X-ray films are
used. As it is recommended that periodical checkups should be strictly
carried out, the number of medical tests currently being conducted is
growing rapidly. On the other hand, more items are included these days in
clinical testing in order to ensure more accurate diagnoses. Both of these
factors have lead to an increase in the number of X-ray images to be
taken. In addition, persons who have received check-ups want to know the
results as soon as possible. In order to meet these demands in the medical
field, not only is it necessary to automate diagnostic procedures (e.g.
imaging and film transport) but it is also required to process X-ray films
more rapidly.
A common method of reducing the length of the processing time (consisting
of development, fixing, washing and drying steps) is to increase the film
transport speed. However, if the roller speed is increased in an attempt
at reducing the processing time required for processing with a roller
transport type automatic processor, several problems occur, such as (a)
insufficient densities (ie, decreased sensitivity, contast and maximum
density), (b) insufficient fixing, (c) insufficient film washing with
water, and (d) insufficient film drying. If fixing and washing are
insufficient, the color of the processed film will change during its
storage to cause image deterioration.
These problems could be solved by reducing the gelatin content but a film
having a lower gelatin content has a tendency to produce a grainy
photographic image. In addition, if films are rubbed against each other or
against another object, the rubbed portion will produce a higher density
than other areas if the film is developed and this phenomenon is generally
referred to as "abrasion blackening".
It is therefore required to realize very rapid processing of photographic
films without causing any of the problems associated with increased roller
speeds or decreased gelatin contents. The term "very rapid processing" as
used in this specification means that the total period of time required
for the film to be transported from the point where its front end is
inserted into an automatic processor and passes through a developer tank,
a transit area, a fixing tank, the next transit area, a washing tank, a
further transit area, and a drying section to the point where it finally
emerges from the last-mentioned section is within the range of from 20 to
60 seconds. The total processing time (sec) may be obtained by dividing
the total length (m) of processing line by the line transport speed
(m/sec). The time required for the film to pass through the three transit
areas is included in the total processing time because, as is well known
in the art, substantial processing is regarded to take place in each of
these transit areas where the gelatin film is also wetted with the
processing solution carried over from the previous step.
Japanese Patent Publication No. 47045/1976 mentions the importance of
gelatin content for the purpose of rapid processing but the total
processing time including passage through transit areas that is attained
by this technique ranges from 60 to 120 seconds, which is longer than is
desirable in a truly "very rapid" processing.
Another requirement that should be met by modern photographic materials is
high sensitivity. For instance, in the wake of the rapid increasing
frequency of medical X-ray testing conducted these days, not only those in
the medical field but also public opinion at large sees a strong need to
reduce the total dose of X-rays to which a patient is exposed and thus the
development of highly sensitive photographic materials which requires
lower X-ray doses to produce images that have sharpness even in fine
detail is desired.
Many and various techniques are available for achieving sensitization, or
providing an increased sensitivity for a given grain size. If an
appropriate sensitization technique is employed, it will be possible to
achieve a higher sensitivity with the grain size (hence the covering
power) being maintained at the same level. Among the sensitization
techniques reported so far are included: addition of a development
accelerator such as a thioether to the emulsion; supersensitizing a
spectrally sensitized silver halide emulsion with an appropriate
combination of dyes; and employing improved optical sensitizers. However,
these methods do not always provide the intended results when they are
applied to high-sensitivity silver halide photographic materials; that is,
if silver halide emulsions intended to be used in high-sensitivity silver
halide photographic materials are treated by these methods, the materials
are liable to experience fogging during storage.
In the field of medical X-ray photography, conventionally used
light-sensitive materials of the regular type having a spectral
sensitivity up to 450 nm are being replaced by ortho-type materials which
have been subjected to orthochromatic sensitization so that they possess
sensitivity up to a wavelength of 540-550 nm. These sensitized materials
not only have an extended spectral sensitivity region but also display
increased sensitivity and hence are effective for the purpose of
minimizing potential hazards to human health by reducing the total dose of
X-rays. Although dye sensitization is a very useful means of
sensitization, many problems still remain unsolved; for instance, the
sensitivity that can be attained is highly dependent on the type of
specific photographic emulsion used.
It is well known to incorporate indazoles or benzotriazoles in a developing
solution as anti-foggants. These compounds have been used as anti-foggants
both in black-and-white developers and in color developers. While the use
of these compounds as anti-foggants is shown in many patent
specifications, three are listed here: U.S. Pat. No. 2,271,229 which
describes the use of an indazole-based anti-foggant in both a
black-and-white developer and in a color developer; BP No. 1,437,053
which discloses the use of an indazole in an X-ray developer as an
anti-foggant; and U.S. Pat. No. 4,172,728 which shows the use of an
indazole in a graphic arts developer as an antifoggant. These indazole and
benzotriazole compounds are very effective anti-foggants, but they still
have the disadvantage of causing a substantial drop in sensitivity.
SUMMARY OF THE INVENTION
An object, therefore, of the present invention is to provide a silver
halide photographic material that can be processed at high speed, even at
a very high speed which is rapid enough to reduce the total processing
time to be within the range of 20-60 seconds, without experiencing any of
the aforementioned problems of the prior art, and which affords high
sensitivity and superior fogging and graininess characteristics, with the
attendant advantage that the gelatin content of the photographic material
can be reduced without causing "abrasion blackening" or desensitization
when subjected to pressure.
Another object of the present invention is to provide a method that is
suitable for processing said photographic material.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic drawing showing an automatic developing machine that
can be used in the practice of the present invention; and
FIG. 2 is a front view of the operating panel on the developing machine of
FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
The first object of the present invention can be attained by a silver
halide photographic material that has at least one hydrophilic colloidal
layer on a support and which is designed to have a water content of 10-20
g/m.sup.2 at the time when the washing step of processing with a roller
transport type automatic processor is completed.
While the water content of the silver halide photographic material of the
present invention can be adjusted to lie within the above-specified range
by a variety of techniques, a typical method consists of adjusting the
melting time of said photographic material to be within the range of 8-45
minutes while controlling the gelatin content of hydrophilic colloidal
layers including light-sensitive silver halide emulsion layers to lie
within the range of 2.00-3.50 g/m.sup.2.
The water content, as defined above, of the photographic material of the
present invention is preferably within the range of 11-18 g/m.sup.2, more
preferably from 12 to 16 g/m.sup.2.
While the photographic material preferably has a melting time of 8-45
minutes, the range of 12-40 minutes is more preferable and the range of
15-30 minutes is most preferable.
The desired melting time may be attained by adjustment with a suitable
hardening agent. To this end, any known hardening agents may be employed
either singly or in admixture. Usable hardening agents are exemplified
below: chromium salts such as chrome alum and chromium acetate; aldehydes
such as formaldehyde, glyoxal and glutaraldehyde; N-methylol compounds
such as dimethylolurea and methylol dimethylhydantoin; dioxane derivatives
such as 2,3-dihydroxydioxane; activated vinyl compounds such as
1,3,5-triacryloylhexahydro-2-triazine and 1,3-vinylsulfonyl-2-propanol;
activated halide compounds such as 2,4-dichloro-6-hydroxy-3-triazine; and
mucohalogenic acids such as mucochloric acid and mucophenoxychloric acid.
Preferably used hardening agents are aldehyde compounds such as
formaldehyde and glyoxal, S-triazine compounds such as
2-hydroxy-4,6-dichlorotriazine sodium salt, and vinyl sulfonic acid
compounds.
The amount of hardening agent used will vary if it is used together with a
hardening accelerator or a hardening inhibitor. A preferable range is from
1.times.10.sup.-6 to 1.times.10.sup.-2 mole per gram of gelatin, with the
range of 5.times.10.sup.-5 to 5.times.10.sup.-3 moles per gram of gelatin
being more preferable.
Typical examples of the hardening agent that can be used in the present
invention are listed below but itshould be understood that the scope of
the present invention is by no means limited by these specific examples.
##STR1##
The second object of the present invention is achieved by a method of
processing a silver halide photographic material having at least one
hydrophilic colloidal layer on a support, said method being so designed
that the water content of the photographic material will lie in the range
of 10-20 g/m.sup.2 at the time when a washing step of processing with a
roller transport type automatic processor is completed.
In a preferred embodiment, the photographic material of the present
invention is processed with a developing solution that contains a compound
of the following general formula (IA) and/or a compound of the following
general formula (IIA):
##STR2##
where R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 each signifies a
hydrogen atom, a lower alkyl group, an alkoxy group, a carboxy group, an
alkoxycarbonyl group, a sulfo group, a halogen atom, an amino group or a
nitro group, each of these groups optionally having one or more
substituents.
Typical examples of the compound of formula (IA) are listed below but it
should be understood that the scope of the present invention is by no
means limited by these examples.
Illustrative compounds of (IA):
I-1: 5-nitroindazole
I-2: 5-aminoindazole
I-3: 5-p-toluensulfonamid-indazole
I-4: 5-chloroindazole
I-5: 5-benzoylacetamino-indazole
I-6: 5-cyanoindazole
I-7: 5-p-nitrobenzoylamino-indazole
I-8: 1-methyl-5-nitro-indazole
I-9: 6-nitroindazole
I-10: 3-methyl-5-nitro-indazole, and
I-11: 4-chloro-5-nitro-indazole.
Among these compounds of formula (IA), nitroindazoles are preferable for
use in the developing solution employed in the present invention, and
5-nitroindazole having the following structural formula is particularly
preferable:
##STR3##
Typical examples of the compound of formula (IIA) are listed below but it
should be understood that the scope of the present invention is by no
means limited by these examples.
##STR4##
The method of the present invention is adapted to very rapid processing of
silver halide photographic materials, and is preferably embodied in
processing with an automatic processor that is completed within a total
period of 20-60 seconds.
In one preferred embodiment of the present invention, the hydrophilic
colloidal layers on the side of a support which has light-sensitive silver
halide emulsion layers has a gelatin content of 2.00-3.50 g/m.sup.2,
preferably 2.40-3.30 g/m.sup.2, more preferably 2.50-3.15 g/m.sup.2,
inclusive of the gelatin in the silver halide emulsion layers. If the
gelatin content is within this range, fewer coating troubles will occur
than when the gelatin content is less than 2.00.sup.2, and better drying
properties are attained than when the gelatin content is larger than 3.10
g/m.sup.2. More preferably, the gelatin content is within the range of
2.40-2.90 g/m.sup.2, with the range of 2.50-2.80 g/m.sup.2 being most
preferable. In accordance with the preferred embodiment described above,
characteristics such as sensitivity and resistance to yellow staining can
be further improved.
In another preferred embodiment of the present invention, the silver halide
grains used in a silver halide emulsion layer have an average size of
0.30-1.20 .mu.m, more preferably 0.40-1.00 .mu.m, with the range of
0.40-0.80 .mu.m being most preferred.
The size of silver halide grains is expressed by the length of one side of
an equivalent cube that has the same volume as that of an individual
grain, and the average grain size is the arithmetic mean of the sizes of
the grains of interest.
In the present invention, silver halide emulsion layers are coated in a wet
thickness which preferably ranges from 35 to 85 .mu.m, more preferably
from 40 to 75 .mu.m, with the range of 45-70 .mu.m being most preferable.
If the wet thickness is excessive, the drying load is increased and it
sometimes becomes necessary to make certain provisions to cope with an
increase in the quantity of heat required for drying or the decrease in
coating speed, which eventually leads to a higher cost and a lower
production rate. If the wet thickness is unduly small, it may become
difficult to achieve uniform and trouble-free coating.
If two or more coating solutions are applied simultaneously onto a support,
the wet thickness as defined in this specification means the total
thickness (.mu.m) of the coated layers in a wet state that form
immediately after the application of those coating solutions (i.e., before
the coating begins to dry). If only one layer is applied at a time, the
wet thickness corresponds to that of a single layer in a wet state that
forms immediately after the application of that layer. The wet thickness
(.mu.m) as defined above may be determined by the following equation:
##EQU1##
If coating is performed in more than one stage (ie, each subsequent coating
is done after the previous coating has dried), the wet thickness as
defined hereinabove means the thickness of the coating solution applied in
each stage.
Still another preferred embodiment of the present invention relates to the
case where two or more hydrophilic colloidal layers are present on the
side of a support which has light-sensitive silver halide emulsion layers;
in this embodiment, the coating solution that will form the topmost layer
is preferably applied in such a manner that it has a surface tension at
least 6 dynes/cm smaller than that of the coating solution which will form
a layer that is adjacent said topmost layer. The difference in surface
tension between the two coating solutions is more preferably at least 8
dynes/cm, with 10 dynes/cm or larger being most preferred.
In order to attain the necessary difference in surface tension, at least
one surfactant may be incorporated in the coating solution which is used
to form the topmost hydrophilic colloidal layer. The coating solution for
forming a layer adjacent this topmost layer may or may not contain a
surfactant, and if a surfactant is used, it may be the same as or
different from the one that is incorporated in the coating solution used
to form the topmost layer.
Useful surfactants include: nonionic surfactants such as saponin (steroid),
alkylene oxide derivatives, glycidol derivatives, aliphatic acid esters of
polyhydric alcohols, and alkyl esters of sugars; anionic surfactants
containing acidic groups such as carboxy, sulfo, phospho, sulfate ester,
and phosphate ester groups; amphoteric surfactants such as amino acids,
aminoalkylsulfonic acids, aminoalkylsulfuric or phosphoric acid esters,
alkylbetaines, and amine oxides; cationic surfactants such as alkylamine
salts, aliphatic or aromatic quaternary ammonium salts, heterocyclic
quaternary ammonium salts such as pyridinium and imidazolium, and
aliphatic or heterocyclic phosphonium or sulfonium salts; as well as
fluorine-containing surfactants which may optionally contain a
polyoxyethylene group.
The silver halide grains used in light-sensitive silver halide emulsion
layers in the photographic material of the present invention may have any
desired grain size distribution. These silver halide grains may be
monodispersed in that 95% of the grains are within 60%, preferably 40%, of
the number average grain size.
The silver halide grains present in light-sensitive silver halide emulsion
layers are preferably such that at least 80% by weight or number of the
silver halide grains concerned have a regular structure or shape. Silver
halide grains having a regular structure or shape are those which grow
isotropically without producing any anisotropically growing surfaces such
as twinned faces; such silver halide grains have cubic, tetradecahedral,
octahedral, dodecahedral or other regular crystallographic forms.
Processes for preparing such regular silver halide grains may be found in,
for example, J. Phot. Sci., 5, 332 (1961), Ber. Bunsenges. Phys. Chem.,
67, 949 (1963), and Intern. Congress Phot. Sic., Tokyo, 1967.
In the practice of the present invention, two or more separately prepared
silver halide emulsions may be used in admixture.
The silver halide grains or silver halide emulsions used in the present
invention preferably contain at least one soluble salt selected from among
the salts of iridium, thallium, palladium, rhodium, zinc, cobalt, uranium,
thorium, strontium, tungsten, and platinum. The content of these soluble
salts is preferably within the range of 10.sup.-6 to 10.sup.-1 mole per
mole of silver halide. It is particularly preferable that at least one of
the salts of thallium, palladium and iridium is contained in the silver
halide grains or emulsions. These salts may be used either singly or in
admixture and they may be added at any state of preparation. By using
these soluble salts, improvement will be achieved in terms of various
characteristics such as flash exposure characteristics, resistance to
desensitization under pressure, resistance to fading of latent images
under exposure to light, and sensitization.
In the practice of the present invention, silver halide emulsions may be
composed of any silver halide that is employed in ordinary silver halide
emulsions, such as silver bromide, silver iodobromide, silver
iodochloride, silver chlorobromide, and silver chloride. The
light-sensitive silver halide emulsion layer contains silver iodide in an
amount of at least 10 mole %.
The silver halide grains in the silver halide emulsions used in the present
invention may be prepared by any known method such as the acid process,
neutral process and ammoniacal process. The grains may be allowed to grow
in one step, or they may be obtained by growth of seed grains. The method
of preparing seed grains may be the same as or different from the one used
to achieve their growth.
In preparing a silver halide emulsion, halide ions and silver ions may be
mixed by simultaneous addition, or either halide or silver ions may be
added to a solution containing the other ions. Alternatively, halide ions
and silver ions may be added simultaneously into a reactor in stages, with
the pH and pAg being controlled in consideration of the critical growth
rate of silver halide crystals. By employing this method, silver halide
grains that have a regular crystallographic shape and a substantially
uniform grain size can be obtained. After their growth, the silver halide
grains may be converted to have a desired halide composition.
It is particularly preferable that the pAg of the silver halide grains
being prepared is adjusted to 9.7 or higher in the latter stage of their
preparation; that is, when at least half the amount of silver to be
prepared has formed or precipitated, the pAg is allowed to change
momentarily or gradually such that it will be at least 9.7 at the time the
preparation is completed. It is more preferable that when the amount of
silver that has formed or precipitated is within the range of from two
thirds to nine tenths of the amount to be prepared, the pAg is allowed to
change gradually such that it will be at least 9.7 at the time when the
preparation is completed.
The silver halide grains used in the present invention may constitute any
proportion of the emulsion layer in which they are present; preferably,
they are present in an amount of at least 40% of the silver in the total
silver halide grains, with the value of at least 90% being particularly
preferable.
The silver halide emulsion used in the present invention may optionally be
prepared in the presence of a silver halide solvent that is effective in
controlling the size, shape, size distribution and growth rate of the
silver halide grains being formed.
Suitable silver halide solvents include ammonia, thioether, thiourea,
thiourea derivatives such as four-substituted thiourea and imidazole
derivatives For thioether, reference may be had to U.S. Pat. Nos.
3,271,157, 3,790,387 and 3,574,628. Silver halide solvents other than
ammonia are preferably used in amounts ranging from 10.sup.-3 to 1.0 wt %,
more preferably from 10.sup.-2 to 10.sup.-1 wt %, of the reaction
solution. The ammonia used as a silver halide solvent may have any
concentration.
During the formation and/or growth of the silver halide grains for use in
the silver halide emulsion used in the present invention, metal ions may
be added in the form of at least one salt selected from among a cadmium
salt, a zinc salt, a thallium salt, an iridium salt (or a complex salt
containing the same), a rhodium salt (or a complex salt containing the
same), and an iron salt (or a complex salt containing the same), so that
one or more of these metal elements are incorporated in the interior of
the grains and/or deposited on their surfaces. Alternatively, reduction
sensitized nuclei may be imparted to the interior and/or onto the surfaces
of grains by placing them in an appropriate reducing atmosphere.
After completion of the growth of silver halide grains, the silver halide
emulsion used in the present invention may be freed of any unwanted
soluble salts; if desired, such soluble salts may be left unremoved from
the emulsion. Removal of unwanted salts may be achieved by employing the
method described in Research Disclosure No. 17643.
The silver halide grains in the silver halide emulsion used in the present
invention may have a uniform distribution of silver halide composition
throughout the interior of the grain; alternatively, they may be of the
core/shell type with different silver halide compositions on the interior
and the surface of their grains.
If the silver halide grains used in the present invention have internal
nuclei that are formed of silver iodobromide, they preferably have a
homogeneous solid solution phase. The term "homogeneous" may be specified
as follows in accordance with the definition set forth in Japanese Patent
Application (OPI) No. 110926/1981 (the symbol OPI as used hereinafter
shall mean an unexamined published Japanese patent application): when a
powder of silver halide grains is subjected to X-ray diffractiometry with
Cu-K.beta. X rays, the peak of the Miller indices [200] for a plane of
silver iodobromide crystal has a half-value width (.DELTA.2.theta.) of no
greater than 0.30 degrees. The operating conditions of the diffractometer
employed may be expressed as .omega.r/.gamma..ltoreq.10, where .omega. is
the scanning speed (deg/min) of a goniometer, r is the time constant
(sec), and Y is the width (mm) of a receiving slit.
The iodine content of the internal nuclei and coating layers of silver
halide grains may be determined by, for example, the method described in
J. I. Goldstein and D. B. Williams, "X-ray analysis in TEM/ATEM", Scanning
Electron Microscopy, 1, 651, published by IIT Research Institute, Mar.
1977.
A silver halide emulsion that may be used in the practice of the present
invention may contain silver halide grains each consisting of an internal
nucleus formed of silver bromide or silver iodobromide, a first coating
layer of silver iodobromide that is formed around the nucleus, and a
second coating layer of silver bromide or silver iodobromide that is
formed around the first coating layer, the iodine content of said first
coating layer being at least 10 mol % larger than that of the internal
nucleus, and the silver in the first coating layer assuming 0.01-30 mol %
of the total silver. In this case, the silver halide grains may be
negative-working, with the surface sensitivity being equal to or higher
than the internal sensitivity, preferably at least twice the latter. The
silver halide grains may be such that the ratio of the size of their
projected area to thickness is less than 5. The size of projected area
means the diameter of an equivalent circle having the same area as the
projected area of a given grain, and the thickness means the length of the
shortest path through the center of gravity of that grain.
If the silver halide grains used in the present invention consist of the
internal nucleus, the first coating layer and the second coating layer
defined above, these components preferably have the following
characteristics: the internal nucleus preferably has an average iodine
content of no more than 10 mol %, preferably 0-5 mol %, with the range of
0-3 mol % being particularly preferable; the silver in the internal
nucleus preferably assumes at least 1.0 mol % of the total silver; the
first coating layer has a silver iodide content which is at least 10 mol %
higher than that of the internal nucleus, with the difference being
preferably at least 20 mol % and more preferably at least 25 mol %; the
silver in the first coating layer preferably assumes 0.1-25 mol %, more
preferably 1.0-15 mol %, and most preferably 3.0-10.0 mol %, of the total
silver.
If the internal nucleus and/or the first coating layer and/or the second
coating layer is formed of silver iodobromide, they need not necessarily
be homogeneous in composition but homogeneity of the silver iodobromide is
preferable. The term "homogeneity" as used hereinabove may be specified as
follows: when a powder of silver halide grains is subjected to X-ray
diffractiometry with Cu-K.beta. X rays, the peak of the Miller indices
[200] for a plane of silver iodobromide crystal has a half-value width
(.DELTA.2.theta.) of no greater than 0.30 degrees. The operating
conditions of the diffractometer meter used may be expressed as
.omega.r/.gamma..ltoreq.10, where .omega. is the scanning speed (deg/min)
of a goniometer, r is the time constant (sec), and .gamma.(mm) is the
width of a receiving slit.
In order to provide sufficient coverage of the first coating layer, the
second coating layer preferably has an average thickness of at least 0.02
.mu.m, more preferably has a silver iodine content of 0-10 mol %.
The silver halide grains described above may constitute any proportion of
the emulsion layer in which they are present; preferably, they are present
in an amount of at 40% of the silver in the total silver halide grains,
with a value of at least 90% being particularly preferable.
The internal nuclei of the silver halide grains described above may be
prepared by various methods such as those described in P. Glafkides,
Chimie et Physique Photographique, Paul Montel, 1967; G. F. Duffin,
Photographic Emulsion Chemistry, The Focal Press, 1966; and V. L. Zelikman
and S. M. Levi, Making and Coating Photographic Emulsions, the Focal
Press, 1964. The acid process, the neutral process or the ammoniacal
process may be employed as required. Soluble silver salts may be reacted
with soluble halide salts by various methods such as the single-jet
method, the double-jet method, and combinations thereof. The "reverse
mixing method" wherein grains are formed in the presence of excess silver
ions may also be employed. One version of the double-jet method is the
controlled double-jet method wherein a silver halide is formed with the
pAg of a liquid phase medium held constant. By employing this method, a
silver halide emulsion comprising grains having a regular crystallographic
shape and a uniform grain size can be attained.
Two or more separately prepared silver halide emulsions may be used in
admixture.
The formation or physical ripening of the internal nuclei of silver halide
grains may be effected in the presence of a cadmium salt, a zinc salt, a
lead salt, a thallium salt, an iridium salt or a complex salt thereof, a
rhodium salt or a complex salt thereof, or an iron salt or a complex iron
salt.
The internal nuclei thus formed may be provided with the first coating
layer by routine methods such as halogen substitution and coating of an
additional silver halide. Halogen substitution may be accomplished by
adding an aqueous solution of an iodide into the reactor where the
internal nuclei have formed. For further information on this method, see
U.S. Pat. Nos. 2,592,250, 4,075,020, Japanese Patent Application (OPI) No.
127549/1980, etc. Coating of an additional silver halide over the internal
nuclei may be accomplished by simultaneous addition of an aqueous solution
of a halide and an aqueous solution of silver nitrate. For further
information on this method, see Japanese Patent Application (OPI) No.
22408/1978, Japanese Patent Publication No. 13162/1968, J. Proto, Sci.,
24, 198 (1976).
After the first coating layer has been formed on the surface of internal
nuclei, the second coating layer may be formed on the first layer by
halogen substitution, coating of an additional silver halide, or any of
the methods that are employed to form the first coating layer.
In preparing the silver halide grains for use in the present invention, any
unwanted soluble salts may be removed from the emulsion in which the
second coating layer has been formed by precipitation or ripened
physically and, if required, from the emulision in which internal nuclei
or the first coating layer has been formed. For this purpose, noodle
washing or flocculation washing may be employed; in noodle washing,
additional gelatin is added to the emulsion, which will solidify into a
jelly upon cooling can can be washed in the form of noodles; in
flocculation washing, inorganic salts, anionic surfactants, anionic
polymers (e.g. polystyrene sulfonic acid), or gelatin derivatives (e.g.
acylated gelatin and carbamoylated gelatin) are used as flocculating
agents.
The silver halide grains used in a silver halide emulsion may be of the
surface image type which forms a latent image predominatntly on the grain
surface or of the internal image type which forms a latent image
predominantly in the interior of the grain.
The silver halide grains used in the present invention may have regular
cyrstallographic shapes such as a cube, octahedron and a tetradecahedron;
alternatively, they may have anomalous shapes such as being spherical or
tabular. These grains may have {100} and {111} faces in any proportion.
The grains may have a combination of these crystallographic shapes, or
they may be a mixture of grains having various crystallographic shapes.
Preferably, the silver halide emulsion that is used in the practice of the
present invention contains silver halide grains at least the surface of
which has {110} crystal faces that are substantially composed of silver
bromide or silver iodobromide. Such a preferably silver halide emulsion
can be prepared by a conventional method of producing a silver halide
emulsion wherein the surfaces of silver halide grains are substantially
formed of silver bromide or silver iodobromide, the only modification
being such that silver halide grains are formed within a aqueous medium
that contains both a hydrophilic protective colloid and a compound that
promotes the development of {110} crystal faces. For instances, by
allowing grains to form in the presence of 1-phenyl-5-mercaptotetrazole
which is conventionally used to stop the growth of silver halide grains,
the development of {110} crystal planes is appreciably promoted to thereby
produce a photographic emulsion that contains {110} faced silver bromide
or silver iodobromide grains.
Mercaptoazoles are preferably used as crystal control compounds, and
mercaptotetrazoles and mercaptothiadiazoles are particularly preferable.
These crystal control compounds may be added at any stage prior to the
completion of formation of silver halide grains (or prior to the
completion of Ostwald ripening). The period of grain formation consists of
two stages, one defined by the start of addition of silver and halide ions
and by the time when the formation of additional nuclei is substantially
finished (this stage may be referred to as the period of nucleation) and
the one which follows the period of nucleation and during which grains
continue to grow with the formation of additional nuclei being
substantially absent (this stage may be referred to as the period of grain
growth). The crystal control compounds are preferably added during the
growth of silver halide grains. The formation of an excessive number of
fine grains can be prevented most effectively by adding crystal control
compounds after the completion of nucleation and prior to the completion
of grain growth. On the other hand, fine silver halide grains can
effectively be produced by using the crystal control compounds either
during or before the period of nucleation.
The crystal control compounds may be charged into the reactor before the
start of silver halide grain preparation; alternatively, they may be added
after crystal precipitation has begun. In the latter case, they may be
added either alone or as a solution in a solvent such as water or an
organic solvent (e.g. methanol or ethanol).
The crystal control compounds may be charged into the reactor either alone
or together with a silver supply solution (e.g. an aqueous solution of
silver nitrate) or as a halide supply solution (e.g. an aqueous solution
of a halide).
The crystal control compounds may be added either continuously or
intermittently. Effective control of crystallographic surfaces can be
achieved if the amount of crystal control compounds added is increased (as
by increasing the amount or concentration of the solution in which they
are present) as the surface area of silver halide grains is increased.
The proportion of the crystallographic surfaces of silver halide grains
taken by {110} faces can be readily modified by changing the amount of
crystal control compounds added. For instance, the proportion of {110}
faces will increase as an increased amount of crystal control compound is
added and it reaches a maximum level within the range of addition to be
specified below. If this range is exceeded, the ratio of {100} planes to
{110} planes will increase
While the amount of crystal control compound added will vary with factors
such as the type of compound used, the conditions of emulsion preparation,
its halide composition and the grain size, a preferable range is from
5.times.10.sup.-5 to 5.times.10.sup.-2 moles per mole of silver halide. A
more preferable range is from 1.times.10.sup.-4 to 1.times.10.sup.-2 moles
per mole of silver halide, with the range of 3.times.10.sup.-4 to
6.times.10.sup.-3 moles being most preferred.
As already mentioned, the silver halide grains suitable for use in the
present invention have {110} crystallographic faces, and at least 20% of
the total surface area of the grains is preferably covered with {110}
faces. It is particularly preferable that at least 80% of the total
surface area of the grains is covered with {110} faces. The presence and
proportion of such {110} faces may be checked by observation under an
electron microscope or by dye adsorption.
The silver halide emulsion used in the present invention preferably
contains at least 30 wt %, more preferably at least 50 wt %, of silver
halide grains having the above-defined proportion of {110} surfaces.
The silver halide grains used in the present invention generally have an
average grain size (the grain size being expressed as the diameter of an
equivalent circle having the same area as the projected area of a grain)
of no more than 5 .mu.m, and the range of 0.1-5 .mu.m is preferable, with
the range of 0.4-2 .mu.m being more preferable.
The silver halide emulsion used in the present invention may have any grain
size distribution. It may be a polydispersed emulsion having a broad size
distribution or it may consist of one or more monodispersed emulsions
having a narrow size distribution. The term "monodispersed emulsion" as
used herein means such an emulsion that the standard deviation of grain
size distribution as divided by the average grain size is no more than
0.20. The grain size refers to the diameter of a silver halide grain if it
is spherical, or to the diameter of an equivalent circle having the same
area as that of the projected image of a non-spherical grain. A
polydispersed emulsion may be used in admixture with a monodispersed
emulsion.
The silver halide emulsion used in the present invention may be a mixture
of two or more separately prepared silver halide emulsions.
The silver halide emulsion used in the present invention may be optically
sensitized for a desired wavelength region using any of the dyes that are
commonly known as sensitizing dyes in the photographic industry.
Sensitizing dyes may be used either independently or in combination with
themselves. Together with sensitizing dyes, dyes that do not themselves
have any spectral sensitizing action or compounds that are substantially
incapable of absorbing visible light and which will enhance the
sensitizing action of sensitizing dyes may be contained in the emulsion.
Useful sensitizing dyes include cyanine dyes, merocyanine dyes, complex
cyanine dyes, complex merocyanine dyes, holopolar cyanine dyes,
hcmicyanine dyes, styryl dyes and hemioxanole dyes. Particularly useful
sensitizing dyes are cyanine dyes, merocyanine dyes and complex
merocyanine dyes. These dyes may contain any of the basic heterocyclic
nuclei that are commonly employed in cyanine dyes; they include pyrroline,
oxazoline, thiazoline, pyrrole, oxazol | | |
